How to Install a Bathtub on Concrete Floor

While a new washbasin can be installed without much effort, the installation of a new bathtub requires more specialist knowledge and special tools.

Above all, even small mistakes can quickly lead to costly flooding. There are two different ways of installing bathtubs: Mounting on a support frame or installation in a bathtub support made of rigid foam.

Table of Contents

General preliminary work

Method 1: Installing a bathtub with tub feet1.1 Mounting the fastening rails1.2 Screw on the feet1.3 Installing the drain and overflow fitting1.4 Anchoring the tub to the wall1.5 Sealing the bathtub1.6. Connecting the bathtub1.7 Sealing the bathtub - Part 21.8 Carry out leak test1.9 Covering the bathtub

The spray area of the bathtub must be waterproof - even if it is tiled afterwards. You must therefore apply a special sealing coat to the wall above the bathtub. Depending on the substrate, it may be necessary to pre-treat the wall with a deep primer beforehand. Place an elastic sealing tape in the corners. You can simply add this to the paint.

Theoretically, you can only apply the paint when the tub is already standing. But I personally think it's better to paint first. Then you can put the paint a little behind the tub and not just above it. On the other hand, you will need the sealing paint for embedding the tub sealing tape again later anyway.

The floor under the bathtub must be level and load-bearing. In the old building and with wooden beam ceilings, which can give way under the weight of the tub, special caution is in demand. Reliable waterproofing is also important to prevent moisture from entering the wooden structure. Here you should talk to an expert beforehand.

Method 1: Installing a bathtub with tub feet

If you have decided to put your bathtub on a secure footing, you will need the bathtub feet that match the bathtub. They are more or less universally applicable, but in the end the devil is often in the detail. To support the bathtub edge, bathtub rails must also be mounted on the wall. These bathtub anchors are often available in a package with the bathtub feet, but can also be purchased separately.

1.1 Mounting the fixing rails

Most bathtub feet consist of fastening rails and adjustable feet. The rails must be screwed to the underside of the bathtub. This works with steel tubs as well as acrylic tubs. Be sure to use the correct screws to avoid damaging the tub.

Where you attach the feet to the underside is up to you. However, make sure that the tub feet do not get in the way of the wall connection or get in the way of the drain installation later on.

1.2 Screw on the feet

Now screw two feet to each rail. However, do not tighten the tub feet yet. First you have to align the tub horizontally after turning it over. Thanks to the adjustable feet, unevenness can be levelled out easily.

So take the spirit level with you and bring the bathtub into a horizontal position. Now you can tighten the screws of the feet.

1.3 Installing the drain and overflow fitting

Now assemble the drain and overflow fittings. Sometimes they are already included in the purchase of the bathtub, for other bathtubs they must be ordered separately.

First take care of the overflow: Mount the profile gasket and the overflow body. Then turn the mounting flange into the overflow body and tighten it. Place the rotary knob on the overflow body.

Now we proceed to the drain: Insert the sealing ring with the screw-in valve into the drain hole from above. Place the suitable seal on the siphon and guide it from below to the drain hole. Now connect the screw-in valve and siphon. In between lies the bathtub.

Connect the overflow pipe and connect the upper drain valve with the siphon. Usually you have to cut it to size.

1.4 Anchoring the tub to the wall

To ensure that the bathtub stands securely later on, you should anchor it to the wall with bathtub strips. On the long side and the short side. Tub strips and tub anchors are required for both acrylic and steel tubs. In addition, the strips are usually equipped with sound insulation. They thus impede sound transmission from the tub body to the wall.

Back to the installation of the bathtub strips: Mark the lower edge of the bathtub edge and then lift the bathtub to the side. Extend the marking on the wall with a spirit level. On both sides.

Place the strips so that their top side touches the marking line. Now you can mark the drill holes. Drill the holes and screw the tub strips to the wall. Note that some wall constructions require special dowels and screws.

Sometimes special clamps are required. Mount them as specified by the manufacturer. Some tub strips are also height-adjustable. Here you can readjust a little later.

1.5 Sealing the bathtub

At the very end, the transitions between bathtub and wall are closed with silicone. However, this does not count as a full seal. Silicone can become friable over time so that moisture can get behind the wall. Therefore a sealing with tub sealing tape is necessary in any case.

So-called tub sealing sets consist of tub sealing tape and sealing corners. First glue the sealing corner to the bathtub. And in such a way that it is flush with the lower edge of the bathtub edge.

If the sealing corner fits, the sealing tapes are connected to it overlapping each other. Cut the tape to fit the length and width of the tub and glue it to the edge of the tub so that it is flush at the bottom.

Now you can glue a sound insulation tape over the trough sealing tapes. It prevents sound transmission from the bathtub to the wall - and vice versa, of course.

1.6 Connecting the bathtub​Now place the bathtub in its final position. Hook the bathtub into the bathtub rails and screw them tight.

Now it becomes particularly important: Connect the drain and overflow fittings to the wall connection. For this purpose, align the drain connection piece on the drain fitting so that it can be connected to the drain in the shortest possible way.

The connection is usually made with HT pipes, which can easily be shortened with a metal saw. Cut edges must be deburred so that small leaks do not occur later.

To ensure that the bath water drains off reliably, a gradient of at least two percent is required between the drain fitting and the wall connection. So that the pipes do not sag, they may have to be underlaid. For example, with hard foam residues or small wooden panels.

1.7 Sealing the bathtub - Part 2

Complete the bathtub seal now. Paint a strip of the wall with liquid seal directly above the bathtub. Fold the sealing tape into the still moist seal and coat the sealing tape with the liquid sealing compound.

Before you do this, you can mask the edge of the tub with soundproofing tape. This way you kill two birds with one stone: you prevent the bathtub edge from getting dirty when you paint it and you can later place the tiles on the tape. After tiling, the tape is pulled out of the joint and filled with silicone.

1.8 Carry out leak test

Before you cover the bathtub, you should check that the pipes are tight. To do this, fill the tub halfway and check that the drain pipe is securely closed.

If everything is in order, let the water run off. Use your hands to check that the pipe connections are all cleanly assembled and sealed. If it drips from one of the connections, you must correct the fault and repeat the leak test until everything remains dry.

1.9 Covering the bathtub

There are basically three ways to cover your bathtub:

•Apron•building slabs•bricklaying

The cladding with an apron is certainly the easiest to realize. It fits exactly to the built-in tub and only needs to be attached to it. No tiles, no sawing - nothing is necessary. For some, however, this is too unstable or you would like a tiled tub, then this is only possible with construction panels or with brick walls.

The cladding with building boards is more laborious. These have to be cut to size and then fixed to the wall, floor and tub. If necessary, you may have to include a revision flap in the area of the drain, but it is not mandatory. But practical in case of an emergency.

The most elaborate, but also the most stable, method is to construct the side wall with bricks. Usually aerated concrete blocks are used for this purpose. They are lightweight and relatively easy to cut to size. And you have to cut a lot if the floor plan of the tub is not straight rectangular.

Method 2: Install bathtub with tub support

Have you decided on a tub support as a substructure for your new bathtub? A good choice. Now you need a suitable support that matches the size and shape of your bathtub. For many popular bathtub models, there is a carrier that fits exactly. But there are also universal supports. Here you have to sabre around more so that the bathtub fits in. But such a universal carrier is usually cheaper.

2.1 Adjusting the carrier

If you have prepared the wall and floor as far as described in the section "General preliminary work", place the tub support in the intended position. Since the girder should not be directly adjacent to the walls, attach the spacers provided for this purpose in front of it. They are simply fastened with the supplied insulation dowels.

In any case, you must remove a piece of polystyrene from the wall outlet. A hand jigsaw is best suited for this. Cut an inspection opening in the area of the outlet. Even if there will be no such opening later after tiling. For the assembly of the tub you need the opening in any case. To prevent the panel from slipping in during tiling, you should guide the saw diagonally inwards when cutting. Adjust the inspection opening to the tile size.

Now place the bathtub in the carrier and check whether everything fits. If yes, then you can continue with the next step. If no, you have to remove parts of the styrofoam. Acrylic tubs, for example, have various bracings and reinforcements on the underside that are obstructive.

To find the right places, simply use a marking spray. Spray the parts of the underside of the bathtub that protrude with the spray and then put the bathtub back in the carrier. The paint will transfer to the polystyrene and you can see exactly where something needs to go.

2.2 Preparing the inlet and outlet fittings

Before lifting the tub out of the carrier, mark the position of the drain on the floor with a pencil. Normally the tub support should already be open below the tub opening. If not, you will need to saw an opening in the support.

Remove the tub and support and lay out the inlet and outlet fittings so that the siphon comes to rest exactly where it is marked. Assemble the set according to the instructions and make a connection to the wall spout.

Make sure that the connection between siphon and spout is as short as possible and has a slight gradient of two percent. The HT pipes are best shortened with a metal saw. Do not forget to deburr afterwards. The tubes must not sag. You can use polystyrene residues or a piece of wood as support.

Now all you have to do is remove the areas of the support where the pipes will later run. Here the marking spray is used again. This marks the pipes and sets the tub support to the desired position. Press lightly and then remove the areas that have become coloured.

2.3 Set tub support

The tub support is firmly bonded to the substrate. This works either with a 2K mounting foam or with tile adhesive.

a) Apply the two-component construction foam to the floor of the support and then carefully place it in its intended position. Align the support horizontally with the spirit level.

b) If tile adhesive is used, first pre-treat the floor with a suitable primer. Once this has dried, apply the tile adhesive to the entire surface of the floor. It is best to use a smoothing trowel with 8 teeth. Now you can place the tub support in the adhesive bed and align it with the spirit level.

2.4 Sealing the bathtub

As with installation on tub feet, the bathtub must also be sealed against the wall when a tub support is used. This is also done with tub sealing tapes, as described in section 1.5.

2.5 Installing the overflow fitting

First you must adjust the length of the overflow pipe. This can usually be done by simply sliding the individual elements together. If everything fits, insert the set into the tub support and screw it to the drain. If you wish, you can also mount the overflow fitting firmly to the bathtub. The screw connection to the drain is then made after the tub has been inserted into the support. This works quite well through the inspection opening.

2.6 Place bathtub in carrier

In order to adapt the bathtub exactly to the shape of the support, you need installation foam. This is applied to the full surface of the tub support edge. In order to be able to remove the tub more easily later, you should first lay a foil on the carrier. It is not necessary to glue the bathtub and carrier firmly together.

Place the bathtub on the mounting adhesive and level it with the spirit level. Then weigh down the bathtub - for example with cement bags. Note that once the adhesive has hardened, no further corrections can be made.

2.7 Sealing bathtubs Part 2

Now finish the tub edge seal as described in section 1.7.

2.8 Installing the drain and overflow fitting

Place the upper part with the sieve from above into the drain of the tub and screw it to the lower part. Mount the control panel on the overflow, which opens and closes the drain. Now test whether you have connected all connections cleanly with each other. Fill the tub with water and feel whether it is dripping somewhere. You can also use a flashlight in hard-to-reach places.

If everything is okay, you can close the opening. Glue the hard foam block with tile adhesive if there should be no inspection opening. Otherwise simply push the polystyrene into the carrier. Now you can tile the tub directly.